The end-users reported that the mechanical properties generally exceeded specifications with two exceptions; although the stress rupture properties of the outer casing manufactured from IN718 for COMAC by both additive manufacturing (AM) and Near Net Shape Hot Isostatic Pressing (NNSHIP) were slightly improved by TWI who modified the heat treatment recommended by COMAC, the properties although improved did not meet specifications. The powder bed gimbal manufactured by ILT (assessed by ILT and not by Collins) distorted and did not meet the specified geometry. In other cases significant post-processing machining was necessary, which impacted on the costs.
The costs of all additive manufacturing (AM) processes and of NNSHIP were significantly higher than current costs and typically it was clear that in some cases machining from the solid would be less costly. On the other hand the investment cast components, produced by IMR and BIAM were either less costly than current technologies or in the case of component 4 (the compressor casing) the cost was identical to that of forging. These conclusions meant that although components could be manufactured, using AM or NNSHIP, the costs precluded the transfer to industry of these technologies for the selected components, other than investment casting. The underlying reason for this conclusion is obvious; the advantages of AM and of NNSHIP lie in the complexity of shapes that can be made and in the case of NNSHIP the additional ability to join different alloys by HIP diffusion bonding so that a component can be made with location-specific properties. Similarly AM can be used to add features to an already existing part and to repair components. The choice of the components by the end-users did not take advantage of the flexibility of manufacture using AM or NNSHIP and thus these technologies were not cost-effective.
Rolls-Royce in particular highlighted the important contribution that modellers had made to optimisation of investment casting of the components made by IMR and BIAM. The modelling of NNSHIP also was confirmed as being capable of producing components that required minimal machining. The difference in the properties of samples taken along the build direction or at 90 degrees to the build direction when using AM to manufacture components is a matter of some concern and as with all powder technologies the influence of inclusions and/or of regions that have not bonded during processing on the reproducibility of properties, was highlighted by end users – in particular by Collins.
Exploitation and dissemination because of the cost of all process-routes, apart from investment casting, the results obtained during EMUSIC will not be directly exploited. There was general support from all of those at the final meeting that we should attempt to build upon the work carried out in EMUSIC, where important cooperation between modellers and processors has been consolidated. If further work is to be done, there needs to be detailed consideration of the factors that could make AM and NNSHIP cost-effective. Complex shapes, adding features to large components and joining of different materials, thus reducing the number of welds required for many engineering components would be obvious areas, which are well-suited to these techniques. Any future research thus requires detailed discussions between end users and those developing/modelling these processes before attempting to put a research proposal together.
